Browsing Theses and Dissertations by Author "Assari, Soroush"
BIOMECHANICAL COMPARISON OF LOCKED PLATING AND SPIRAL BLADE RETROGRADE NAILING OF SUPRACONDYLAR FEMUR FRACTURESDarvish, Kurosh; Rehman, Saqib; Pillapakkam, Shriram (Temple University. Libraries, 2011)Background: Comminuted supracondylar femur fractures in the elderly are often treated with either retrograde femoral nailing or locked plating. Early weight-bearing is typically restricted after fixing supracondylar fractures, thereby impairing the patient's mobilization. In general, surgeons are more comfortable allowing early weight-bearing of long bone fractures after nailing rather than plating, but early studies of retrograde nails for supracondylar fractures using standard distal locking showed poor fixation compared with locked plating. Newer generation distal locking techniques, such as the spiral blade, may demonstrate improved fixation, potentially allowing early weight bearing. The purpose of this study is to biomechanically compare locked plating with retrograde nailing of osteoporotic supracondylar femur fractures with simulated physiologic weight-bearing in the post-operative period. Methods: The Locking Condylar Plate (LCP) and Retrograde/Antegrade EX Femoral Nail (RAFN) with spiral blade locking were tested using 10 paired elderly cadaveric femurs, divided into normal and low BMD groups, with a simulated AO/OTA type 33-A3 supracondylar femur fracture. Each specimen was subjected to 200,000 loading cycles simulating six weeks of postoperative recovery with full weight-bearing for an average individual and the construct subsidence and axial stiffness were measured. Results: LCP fixation compared to RAFN showed higher axial stiffness for normal and low BMD groups (80% and 57% respectively). After cyclic loading, axial stiffness of both constructs decreased by 20% and RAFN fixation resulted in twice as much subsidence (1.9±0.6 mm). Two RAFN constructs with low BMD failed after a few cycles whereas the matched pairs fixed with LCP failed after 68,000 and 100,000 cycles. Conclusions: The LCP construct was stiffer than RAFN construct. Early weight bearing may cause 3-4 mm of subsidence in elderly patients with low BMD. However, because of the observed failures in two of the samples treated with RAFN in the low BMD group, early weight bearing is not recommended in osteoporotic bones treated with RAFN.
BLAST-INDUCED CEREBROVASCULAR AND BRAIN INJURY: THE THORACIC MECHANISMDarvish, Kurosh; Kiani, Mohammad F.; Barbe, Mary F.; Galie, Peter (Temple University. Libraries, 2017)The focus of this dissertation was the biomechanics of blast-induced traumatic brain injury (bTBI). This study had three specific aims. One of the specific aims was to investigate the thoracic mechanism of bTBI by characterizing the cerebral blood pressure change during local blast exposure to head or chest in a rat model. This model utilized a shock tube to simulate the blast wave. The results showed that there is a blood pressure rise with high amplitude and short duration during both Head-Only and Chest-Only exposure conditions. It was shown that cerebral blood pressure rise was significantly higher in Chest-Only exposure, and resulted in astrocyte reactivation, and infiltration of blood-borne macrophages into the brain. It was concluded that due to chest exposure to a blast wave, high amplitude pressure waves that transfer from thoracic large vessels to cerebrovasculature can lead to blood-brain barrier disruption or perivascular injury and consequently trigger secondary neuronal damage. The second and third aims were related to the viscoelasticity and heterogeneity of brain tissue respectively for blast rate loading conditions. For the second specific aim, a novel test method was developed to apply shear deformation to samples of brain tissue with strain rates in the range of 300 to 1000 s-1. The results of shear tests on cylindrical samples of bovine brain showed that the instantaneous shear modulus (about 6 kPa) increased about 3 times compared to the values reported in the literature. For the third specific aim, local viscoelastic behavior of rat brain was characterized using a micro-indentation setup with the spatial resolution of 350 mm. The results of micro-indentation tests showed that the heterogeneity of brain tissue was more pronounced in long-term shear moduli. Moreover, the inner anatomical regions were generally more compliant than the outer regions and the gray matter generally exhibited a stiffer response than the white matter. The results of this study can enhance the prediction of brain injury in finite element models of TBI in general and models of bTBI in particular. These results contribute to development of more biofidelic models that can determine the extent and severity of injury in blast loadings. Such predictions are essential for designing better injury mitigation devices for soldiers and also for improving neurosurgical procedures among other applications.